Reverse osmosis is a process useful for desalinization of seawater as well as treating other liquids and is a process in which a pressure gradient across a semipermeable membrane can force water from an aqueous solution through the semipermeable membrane leaving a more concentrated effluent on one side of the membrane. The pressure required to overcome the osmotic pressure of the solution depends on the salts in the solution and hence becomes greater as the solution becomes more concentrated on the one side of the membrane. For seawater, a pressure typically in the range of from about 600 to about 1,000 psi is necessary to effect the reverse osmosis process. For solutions other than seawater, a different pressure gradient across the membrane will be required, all as is well known in the art.
An increasing use has developed in home, factory and office for units providing purified water from ordinary tapwater which may be hard water or well water, making use of a reverse osmosis filter. These filters produce purified water which is good for drinking or other purposes, as well as a larger quantity of effluent containing a higher concentration of impurities or contaminants than the incoming water. Because of the slow rate of flow of purified water through these filters, the purifying system may include storage tanks to retain the purified water and controls for directing the purified water to and from the tanks. Many of these designs are bulky and expensive.